This invention relates to an extraction zone for a solid fuel burner, In particular, but not exclusively, to a solid fuel burner of the type where a primary chamber receives a solid fuel which can be of any type such as wood, biomass such as straw, coconut shell or husk, briquetted sawdust, bark chips, wood logs or billets for example. The solid fuel is gasified by a controlled combustion in the primary chamber and the resulting gas is received, and further combusted, in a secondary combustion chamber which produces a high temperature gas exhaust which can be used for any suitable heating purpose. The extraction zone of the present invention connects the above mentioned primary and secondary chambers.
Such solid fuel burners with which the present invention can be used are suitable for a variety of purposes. These may be; direct heat applications in the heating and drying of agricultural produce such as tea, coffee, cocoa, copra, grain; industrial heating applications such as the heating of glasshouses, kilns and industrial premises; indirect heating applications such as the heating of heat exchange tubes of a heat exchanger or the heating of water or any other medium also by means of an appropriate heat exchanger.
In many instances such solid fuel burners can be used efficiently as a replacement for, or conversion of, existing diesel, electric or gas fired systems.
To the present time, solid fuel burners of this type have had problems in achieving an efficient transfer of gas from the primary chamber to the secondary chamber. This is particularly due to the ducting connecting the primary chamber to the secondary chamber being provided in the past typically by a number of transverse tubes extending across the bottom end of the primary chamber through which the heated gasified fuel has needed to pass in reaching the secondary chamber. However, the fuel within the primary chamber has tended to block off these transverse tubes and in so doing has constrained the entry of the gasified fuel into the secondary chamber. Also, fuel and particulate matter has tended to be drawn into the secondary chamber. This increases the likelihood of sparks being produced in the secondary chamber exhaust and causing problems particularly where the hot gas is used for drying purposes in explosive dusty situations.
Moreover, in previous types of burners a large quantity of induced draught was required at a large velocity. This resulted in "slagging" of the refractory material in the burner, i.e. the depositing of material on the refractory material, thus closing off the gas flow paths in a relatively short period of time.
It is thus an object of the present invention to provide an extraction zone between the primary and secondary chambers of a solid fuel burner which can achieve an efficient transfer of gasified fuel between these chambers and which overcomes or at least obviates the problems associated with such transfer in existing types of solid fuel burners.
Further objects of the present invention will become apparent from the following description.